For example, a high intensity discharge lamp (HID lamp) such as a xenon lamp and an extra-high pressure mercury lamp has been used so far, in a projector for image display such as a DLP™ projector and a liquid crystal projector, and a photo mask exposure apparatus. As an example, the principle of such a projector is shown in FIG. 21 (reference: Japanese Patent Application Publication No. 2004-252112 etc.).
As described above, light from a light source (SjA), which is made up of a high intensity discharge lamp etc., is inputted into an incident end (PmiA) of a light uniformizing unit (FmA) by, for example, using a condensing unit (not shown), which is made up of a concave reflection mirror, a lens, etc., and is outputted from an emission end (PmoA) thereof. Here, for example, an optical guide can be used as the light uniformizing unit (FmA), which is also called a rod integrator, a light tunnel, etc., and is formed of a prism made from light transmissive material such as glass, resin, etc., wherein while the light inputted into the incident end (PmiA) is repeatedly and totally reflected on side faces of the light uniformizing unit (FmA) according to the principle, which is the same as that of an optical fiber, it propagates inside the light uniformizing unit (FmA), thereby functioning so that the illuminance on the emission end (PmoA) is sufficiently uniformized even if distribution of the light inputted into the incident end (PmiA) has unevenness.
With respect to an optical guide described above, in addition to the optical guide which is a prism shape and is made from light transmissive material such as glass, resin, etc. there is another type of optical guide, which is a hollow prism shape wherein the inside thereof is made up of a reflecting mirror, and light propagates, repeating a reflection thereinside in a similar manner thereby achieving the same function.
An illumination lens (Ej1A) is arranged so that a quadrangle image of the emission end (PmoA) is formed on a two-dimensional light amplitude modulation element (DmjA), whereby the two-dimensional light amplitude modulation element (DmjA) is illuminated by light outputted from the emission end (PmoA). However, in FIG. 21, a mirror (MjA) is arranged between the illumination lens (Ej1A) and the two-dimensional light amplitude modulation element (DmjA). And the two-dimensional light amplitude modulation element (DmjA) modulates light on a pixel to pixel basis according to an image signal so that the light is directed so as to enter the projection lens (Ej2A), or light is directed so as not to enter there, whereby an image is displayed on a screen (Tj).
Since the above-described two-dimensional light amplitude modulation element is also called a light valve, and in the case of the optical system shown in FIG. 21, a DMD™ (Digital Micromirror Device) is generally used as the two-dimensional light amplitude modulation element (DmjA).
The so-called fly eye integrator may be used as the light uniformizing unit, instead of the above-described optical guide. FIG. 22 shows the principle of a projector using this light uniformizing unit, as an example (reference: Japanese Patent Application Publication No. 2001-142141 etc.).
Light from a light source (SjB), which is made up of a high intensity discharge lamp etc., is inputted, as approximately parallel light flux, into an incident end (PmiB) of a light uniformizing unit (FmB) which is made up of a fly eye integrator, by using a collimator unit (not shown), which consists of a concave reflection mirror, a lens, etc. and is outputted from an emission end (PmoB). Here, the light uniformizing unit (FmB) is made up of a combination of an upstream fly eye lens (F1B) on an incident side, a downstream fly eye lens (F2B) on a light emission side, and an illumination lens (Ej1B). The upstream fly eye lens (F1B) and the downstream fly eye lens (F2B) are respectively formed by arranging, in vertical and horizontal directions, many quadrangle lenses whose focal distance is the same as one another and whose shape is the same as one another.
Each lens of the upstream fly eye lens (F1B), and each corresponding lens of the downstream fly eye lens (F2B), which is located downstream of each lens of the upstream fly eye lens (F1B), form an optical system called Koehler illumination, so that many Koehler illumination optical systems are aligned in a matrix in a plane. Generally, such a Koehler illumination optical system is made up of two lenses, wherein when the upstream fly eye lens collects light and illuminates an object face (a face to be illuminated), the upstream lens does not form an image of a light source on the object face, but forms an image of the light source on a center face of the downstream lens, whereby the object face is uniformly illuminated by arranging the downstream lens so as to form a quadrangle contour image of the upstream lens on the object face. The downstream lens functions so as to prevent a phenomenon in which an illuminance of a circumference part of the quadrangle object face falls depending on the size, if the downstream lens is not provided and a light source is not a perfect point light source but has a limited size, whereby it is possible to form a uniform illuminance on even the circumference part of the quadrangle object face by the downstream lens, independent of the size of the light source.
Here, since the optical system shown in FIG. 22 is configured based on case where approximately parallel light flux is inputted into the light uniformizing unit (FmB), an interval between the upstream fly eye lens (F1B) and the downstream fly eye lens (F2B) is set so as to become equal to those focal distances, so that an image of the object face of the uniform illumination of a Koehler illumination optical system is formed at infinity. However, since an illumination lens (Ej1B) is arranged downstream of the downstream fly eye lens (F2B), the object face can be pulled near on the focal plane of the illumination lens (Ej1B) from the infinity. Since the Koehler illumination optical systems arranged in a matrix in a plane are parallel to an incident light axis (ZiB) and light flux is approximately axisymmetrically inputted therein with respect to each central axis so that the output light flux is also approximately axisymmetrical, and the outputs of all the Koehler illumination optical systems are imaged on the same object face on the focal plane of the illumination lens (Ej1B) because of the nature of lens, i.e., a Fourier transform of a lens, in which light rays entering a lens face at the same angle as one another, are refracted so as to be directed to the same point on a focal plane without depending on the incidence position on the lens face.
As a result, all the illuminance distributions in lens faces of the upstream fly eye lens (F1B) are overlaid, so that one synthesized quadrangle image, whose illuminance distribution is more uniform than that in case of one Koehler illumination optical system, is formed on the incident light axis (ZiB). The two-dimensional light amplitude modulation element (DmjB), which is an illumination object, is illuminated by light outputted from the emission end (PmoB) when a two-dimensional light amplitude modulation element (DmjB) is arranged at a position of the synthesized quadrangle image. However, a polarization beam splitter (MjB) is arranged between the illumination lens (Ej1B) and the two-dimensional light amplitude modulation element (DmjB) so that the light is reflected towards the two-dimensional light amplitude modulation element (DmjB) when the light is illuminated. And the two-dimensional light amplitude modulation element (DmjB) performs a modulation and reflection so as to or so as not to rotate the polarization direction of the light by 90 degrees on a pixel to pixel basis according to an image signal, whereby only the rotated light passes through the polarization beam splitter (MjB), and enters the projection lens (Ej3B), so that an image may be displayed on a screen (Tj).
In addition, in the case of the optical system shown in FIG. 22, in general, a LCOS™ (Liquid Crystal on Silicon) is used as the two-dimensional light amplitude modulation element (DmjA) in many cases. In the case of such a liquid crystal device, since only a component of light in a specified polarization direction cannot be modulated effectively, although a component parallel to the specified polarization direction is usually passed therethrough as it is, only a component perpendicular to the specified polarization direction is rotated by 90 degrees with respect to the polarization direction, so that the polarized-light alignment functional device (PcB) for making all the light effectively usable is inserted, for example, downstream of the downstream fly eye lens (F2B). Moreover, a field lens (Ej2B) is inserted immediately upstream of the two-dimensional light amplitude modulation element (DmjB) so that approximately parallel light may enter the two-dimensional light amplitude modulation element (DmjB).
In addition to the reflection type of the two-dimensional light amplitude modulation element shown in FIG. 22, a transmissive liquid crystal device (LCD) may be used as the two-dimensional light amplitude modulation element in the optical arrangement which is suitable therefor (reference: Japanese Patent Application Publication No. H10-133303 etc.).
Generally, for example, a dynamic color filter such as a color wheel is arranged upstream or downstream of the light uniformizing unit in a projector in order to display a color image, and the two-dimensional light amplitude modulation element is illuminated with color sequential light flux of R, G and B (Red, Green, Blue), whereby color display is realized in time dividing manner, or a dichroic mirror or a dichroic prism is arranged downstream of the light uniformizing unit, so that the two-dimensional light amplitude modulation element, which is independently provided in each color, is illuminated with light which is separated into the three primary colors of R, G and B, and a dichroic mirror or a dichroic prism for performing color synthesis of the modulated light flux of the primary colors R, G and B is arranged. However, for ease of explanation, in FIGS. 17, 18A and 18B, these elements are omitted.
However, the high intensity discharge lamp has drawbacks such as low conversion efficiency from applied power to light power, i.e., great calorific, and a short life span. A solid light source such as an LED and a semiconductor laser attracts attention in recent years as an alternative light source, in which these drawbacks are solved. Although of these light sources, calorific loss of the LED is smaller and an operating life span thereof is longer than those of the discharge lamps, since there is no directivity of light emitted therefrom as in the discharge lamps, there is a problem that the usage efficiency of light is low when it is used in the above-mentioned projector or exposure apparatus, in which only light in specific direction can be used.
On the other hand, since a semiconductor laser has high directivity in addition to a small calorific loss and a long operating life spam as in such an LED, while there is an advantage that the usage efficiency of light is high, when it is used in the above-mentioned projector, exposure apparatus, etc. in which only light in a specific direction can be used, there is a problem that a speckle occurs. Here, the “speckle” means a granular/patchy pattern, which inevitably appears when projecting light of a semiconductor laser or another type of laser, or coherent light which is generated by performing wavelength conversion of laser light (by using nonlinear optical phenomena, such as a harmonic generation and an optical parametric effect). However, where it is used for generation of a viewing image in, for example, a projector, and for precise exposure of a photomask pattern on a film which is made from photosensitive material, there is a very troublesome phenomenon in which the quality of image is remarkably degraded, so that many devices for an improvement thereof have been proposed for many years.
For example, Japanese Patent Application Publication No. S59-024823 teaches an influence elimination apparatus of speckle of an output light of an optical fiber, in which an optical element for changing the relative relation between an input end face of the optical fiber and a laser optical beam in terms of time, is inserted inside an optical path of the optical fiber whose input end face receives a laser beam which is formed by condensing laser light. The patent application publication teaches, as an example, one form of changing the relative relation between the input end face of the optical fiber and the laser optical beam in terms of time, in which the position of a spot on the input end face of the optical fiber, at which the laser optical beam is condensed, is changed within a predetermined range in a vibrating manner, wherein an optical system configuration, using an ultrasonic diffraction element, a deflecting mirror (galvanometer), an oscillating mirror, and a rotation non-parallel glass plate is given as embodiments.
The patent application publication teaches, as an example, one form of changing the relative relation between the input end face of the optical fiber and the laser optical beam in terms of time, wherein although the position of a spot on the input end face of an optical fiber, at which the laser optical beam is condensed, is not changed, the angle of the central axis of the condensing laser optical beam is changed within a predetermined range in a vibrating manner. However, no concrete optical system configuration has been proposed.
On the other hand, in case where a periodic perturbation is added to a dynamic mechanism, specifically a route of an a propagation path of light in an optical system or a light path length in the propagation path, thereby periodically changing the phase distribution of the light on a face to be irradiated, if an element, which performs periodic operation, is contained in the structure of the apparatus using an illumination light, for example, a beat phenomenon arises due to an interference of periodicity of both, that is, frequency difference of both in an periodic operation, so that there is possibility that light having frequency, at which man can view it, changes.
For example, in the case of the projector shown in FIGS. 21 and 22, since in an operation of the two-dimensional light amplitude modulation element (DmjA) or the two-dimensional light amplitude modulation element (DmjB), not only a component of spatial modulation but also periodic modulation, namely, a component of a time-periodic modulation in a segment of time, is contained, if, as described above, a light source, which is configured so that a periodic perturbation is added to a route of a propagation path of light or the light path length in the propagation path, is used, a flicker etc. may occur in the whole image to be displayed or a specific hue or specific brightness. However, no solution has been proposed to solve this problem.